BoneKEy Reports | BoneKEy Watch

Characterizing osteoblasts and MSCs using in vivo techniques

---

DOI:10.1038/bonekey.2012.87

Mesenchymal stem cells (MSCs) in bone tissue are already being trialled as potential therapeutic tools in patients with bone fractures or skeletal disorders. Park et al., who highlight that MSCs have, thus far, only been defined by their behavior in vitro, designed a series of in vivo experiments in mice to follow and characterize Mx1+ stromal cells that exhibit many of the expected features of MSCs.

Using pulse-chase tracking and two-photo/confocal hybrid microscopy, they tracked the Mx1+ cells in live animals over time. This revealed that osteoblasts are actually not able to divide, and live for a maximum of 60 days in the bone marrow. They are replenished by a pool of cells expressing Mx1, which are also able to translocate to a fracture site where they multiply and mature. Chondrocytes that are active in bone repair seem to be from a different lineage.

Editor's comment: This is a very detailed study that employs a series of elegant reporter systems and in vivo imaging to demonstrate that mature osteoblasts do not proliferate and replace cells in bone, but are short lived and do not play a role in fracture healing. The researchers' methods and use of genetic tools for pulse-chase lineage tracking are outstanding.

---

This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License.